According to Dr. Carmela Tartaglia, a clinician-scientist at University Health Network and associate professor at the University of Toronto, young onset Alzheimer’s disease is often overlooked and misdiagnosed as depression or a midlife crisis. This is largely because the illness can present itself differently in younger patients, and doctors don’t always think “dementia” when they see someone in their 40s or 50s.

WATCH BELOW: Ask the doctor: What is dementia?

“If you’re 75 and you tell me that your memory is not great, people are saying you’ve changed, and you’re easily overwhelmed, … we Alzheimer’s disease,” Tartaglia told Global News. “When you’re 55 and coming in with those complaints, people will say, ‘Oh, you’re probably depressed.'”

“You don’t put Alzheimer’s on the top of that list.”

A lack of public awareness around young onset dementia contributes to misdiagnoses, but Tartaglia also said there’s a tendency for younger people to have atypical symptoms.

“Some of these people will present with a language problem,” Tartaglia said. “Their visual memory can be fine, they can be OK with recalling recent events, but their big problem is that their memory for words is not what it used to be.”

Another symptom of young onset dementia is visual processing problems, including not being able to understand an environment the same way as before.

“People will be looking for things, and the things are right in front of them but they can’t find them,” Tartaglia said. “Or, they’re trying to type something, but the wrong letter keeps coming up.”

“I had one who is 50 years old and an IT specialist. He had been doing for decades, and he kept making mistakes over and over again. He was wondering why his fingers weren’t ending up on the right keys.”

A reason why younger people might exhibit different symptoms than those in their 80s is because the disease can affect different parts of the brain, Tartaglia said. While researchers don’t understand why some people experience memory loss while others have trouble remembering a word, the underlying cause of Alzheimer’s disease is the same: abnormal deposits of protein in the brain that become toxic to brain cells.

Another factor that contributes to people being diagnosed with depression instead of dementia is overlapping symptoms. People who are experiencing dementia may became apathetic or withdrawn, much like those suffering from a mood disorder.

“You may feel overwhelmed, and feel like you can’t get the right words out, so you don’t want to be in social situations that much anymore,” Tartaglia explained. “You can withdraw from things.”

Plus, since many people in their 40s and 50s are still working, their symptoms might be attributed to a hectic schedule or demanding lifestyle.

So how can you tell the difference between young onset dementia and depression? Watch for ongoing evidence of symptoms, and note if they’re getting worse. Diseases of the brain don’t get better, Tartaglia said.

“Consistent problems with memory, consistent problems with organization. … if this is a problem happening over and over again,” she said. “If you see a real personality change in someone … you need to pay attention to that.”

Tartaglia said if you suspect you or someone you know is experiencing young onset dementia, it’s important to see a doctor.

“With Alzheimer’s disease, you can test for it when a person is alive,” she said. “We’re hoping that these misdiagnoses are going to stop happening because when you realize somebody might have and it’s not just a midlife crisis … you have them tested.”